Liquid crystals are used primarily as dielectrics in indicating devices, since the optical properties of such substances can be influenced by an applied voltage. Electro-optical devices based on liquid crystals are well-known to a person skilled in the art and can be based on various effects. Examples of such devices are cells having dynamic scattering, DAP cells (deformation of aligned phases), SSF cells (surface stabilized ferroelectric), DHF cells (deformed helix ferroelectric) or SBF cells (short-pitch bistable ferroelectric).
The liquid crystal materials must have a good chemical and thermal stability and a good stability towards electric fields and electromagnetic radiation. Further, the liquid crystal materials should have low viscosity and in the cells should give short response times and a high contrast. Furthermore, at usual operating temperatures of about -30.degree. C. to about +80.degree. C., especially of about -20.degree. C., to about +60.degree. C., they should have a suitable mesophase, for example a broad smectic mesophase for the cells referred to above.
Since liquid crystals are usually used as mixtures of several components, it is important that the components have a good miscibility with one another.